Printed from: Quest Integrity
http://www.questintegrity.com/

Print

Articles

Problem Solving in the North Sea

By: Stefan Papenfuss, Vice President, Pipeline Resources

As seen in the August 2014 issue of World Pipelines Magazine. Download the PDF version.

Recently, a major exploration and
production company faced a challenging situation to complete an integrity
inspection on an offshore production-to-storage pipeline in the North Sea. The project
included the inspection of one 10-inch (254 mm) diameter pipeline to obtain the
wall loss and geometry data needed to assess the pipeline’s integrity. The challenges included low-flow conditions, vertical
launching and limited platform space, situations that would typically require
front-end line, process and tool modifications to run an inspection tool. The
company reached out to Quest Integrity Group to solve this difficult in-line
inspection (ILI) project.

"The challenge to the client was to complete
the inspection and integrity assessment of a low-flow production line with
limited access in the North Sea. The fact that the line is offshore and subsea
always creates another level of complexity compared to onshore operations,”
explains Jason Tuer, Quest Integrity’s Technical Advisor for the project.

Project Details

The pipeline inspection project
presented two major challenges. First, the pipeline flow was exceedingly slow,
by about a factor of ten. Quest Integrity Group overcame this challenge using
the InVista™ ultrasonic in-line inspection technology. "Most of the ILI tools
on the market cannot run at such a slow pace,” said Tuer, "but Quest
Integrity’s ILI tool does. The inherent features of the technology allow the
equipment to work extremely well in low-flow conditions.”

The second challenge was the
vertical launch. Since the tool is very
compact, it doesn’t take up a lot of space on the platform deck and it is very
lightweight, which allows it to be launched from a vertical position with no
specialized handling required. "Fortunately, no newly engineered, developed or
designed tool was needed,” says Tuer. "Quest Integrity was able to complete the
inspection and integrity assessment using the standard design InVista tool.”

Typical Offshore Production Platform

Prior to engaging with Quest
Integrity, the client set the scope of services for the project, which included
geometry data on the line. The client
assumed that would require a separate caliper inspection, which would have been
difficult given the operational conditions. However, Quest Integrity’s ILI tool provides complete wall loss and
geometry dataÂ­, therefore there was no need to perform a separate caliper survey.

Quest Integrity traveled to the offshore
platform and met with the client’s staff to begin preparations for the
inspection. As part of standard
operating procedure for offshore projects, Quest Integrity arrived in advance
of the actual inspection start date. The early arrival allowed the project
manager to witness the final stages of the cleaning campaign and assist in
final cleaning tool configurations to ensure that the line was sufficiently
clean prior to introducing the ILI tool into the line.

The tool was propelled at a pressure of 6/7 barg, which
translates to a speed of 91.44 mm per second (0.30 feet per second). It traveled the entire length of the pipeline
and was received at the wellhead platform receiver.

After determining that the
recorded data was mostly free of anomalies associated with scaling, gas pockets
or other foreign material, the data was downloaded and prepared for the
preliminary API 579-1/ASME FFS-1 2007 fitness-for-service assessment. This preliminary report was delivered to the
client within hours of the inspection.

Inspection Results and
Fitness-for-Service Assessment

Following the field inspection
data verification and preliminary report, the pipeline inspection data was
analyzed for wall thinning and anomalies such as corrosion, denting, and
ovality and the fitness-for-service of the pipeline was determined. The
assessment was based on the longitudinal extent of thinning found in the
pipeline and in accordance with a Level 2 Assessment described in Part 5 of the
API 579 standard. The data can be viewed
and assessed using LifeQuestTM Pipeline software, and the remaining
strength factor (RSF) and reduced maximum allowable operating pressure (MAOPr) were
also reported for the pipeline.

Table 1 represents a summary of
the quality of data analyzed, the calculated RSFs, and compares computed MAOPr
values for the pipeline to the maximum operating pressure provided by the
exploration and production company.

· A total of 19 external and manufacturing related
metal loss anomalies were individually identified in the inspection data. The
minimum measured thickness due to external metal loss was 13.1mm (0.516 in.).
Based upon a nominal wall thickness of 20.6mm (0.811 in.), this metal loss
corresponds to a 36.4% wall loss.

· No internal metal loss anomalies were
individually identified in the inspection data.

· A total of 17 dents in excess of 0.5% of the
nominal outer diameter (OD) were identified in the inspection data. The maximum
dent size was 2.2% of nominal OD and was located at 2966.22m (9731.7 ft.),
between girth welds #2700 and #2710.

· The minimum reduced MAOP calculated, according
to the Part 5 Level 2 assessment methodology in API 579, was 28,220 KPa (4,093
psi).

LifeQuest™ Pipeline 2D and 3D Images of External Metal Loss on the
Line

Based upon the inspection data,
the pipeline was found to satisfy the API 579 Part 5 Level 2 fitness-for-
service criteria for any maximum operating pressures equal to or below the
listed MAOP of 12,400 kPa (1,798 psi).

Also, the inspection identified no
dents on the pipeline in excess of 6% of the nominal OD, no metal loss in
excess of 80% wall loss, and no dents with associated metal loss. The inspection
revealed that the ASME modified B31G maximum depth criterion of 80% was not
exceeded for the pipeline. The lowest Psafe value, based on the original B31G
equation, was 30,588 KPa (4,436 psi), which was greater than the listed design
MAOP of 12,400 kPa (1798 psig).

The report noted that the
assessment calculations were performed without any future corrosion allowance
and that all calculations stated in the report did not reflect tool tolerance. The
final report recommended future inspection to monitor corrosion rates to the
client, and that additional assessment to analyze the damage mechanisms or to
more accurately quantify the stresses (e.g. Level 3 analysis) experienced by
the thinned areas, could provide greater confidence for the continued safe
operation of the pipeline.

"Using the InVista ILI tool, we were able to
gather an abundant amount of data,” says Tuer. "The project resulted in a
detailed final data set for the client’s service department.”

Benefits to the
Client

By utilizing the InVista tool, Quest
Integrity created additional value for the client because no front-end tool, line
or operational modifications were required in order to run the tool. Heavier
and longer ILI tools requiring specialized handling would have increased
project costs and HSE concerns. Caliper tool runs would also be required if
both the geometry and wall loss data could not be collected by the same tool in
one run. In addition, a gauge tool run is traditionally a safety measure ahead
of an ILI run to make sure the line is unobstructed, but due to the high
collapsibility factor of the tool, it was not necessary.

"We could literally get onto the platform
without special permits or concessions that would have had to be made with
other larger or unwieldy tools,” explains Tuer. "The fact that the tool is
extremely lightweight and easy to handle means there is limited risk to
inspectors involved in the operation. This translates into an increased
emphasis on safety, because the operator did not have to use the type of
cumbersome tool that is traditionally used in pipeline inspections.” By utilizing
lightweight and compact equipment within confined spaces in an offshore
environment, operators can mitigate risk for in-line inspections.